what is unreinforced masonry?

Unreinforced Masonry Buildings and Earthquakes Developing Successful Risk Reduction Programs FEMA P-774 / October 2009 FEMA

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Page 1: What is Unreinforced Masonry?

Unreinforced MasonryBuildings and EarthquakesDeveloping Successful RiskReduction Programs

FEMA P-774 / October 2009


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Th e cover photos show signifi cant damage to unreinforced masonry buildings that resulted from earthquakes occurring over the last century, across the country.

Front Cover Photo Credits (clockwise from top left):

1886, Charleston, South Carolina: J. K. Hillers, U.S. Geological Survey

2003, San Simeon, California: Josh Marrow, Earthquake Engineering Research Institute Reconnaissance Team

2001, Nisqually, Washington: Oregon Department of Geology and Mineral Industries

1935, Helena, Montana: L. H. Jorud, courtesy of Montana Historical Society and Montana Bureau of Mines & Geology

1993, Klamath Falls, Oregon: Oregon Department of Geology and Mineral Industries

2008, Wells, Nevada: Craig dePolo, Wells Earthquake Portal, www.nbmg.unr.edu/WellsEQ/.

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Unreinforced Masonry Buildings and Earthquakes

Developing Successful Risk Reduction Programs

FEMA P-774/October 2009

Prepared for:Federal Emergency Management Agency (FEMA)

Cathleen Carlisle, Project MonitorWashington, D.C.

Prepared by:Applied Technology Council (ATC)

201 Redwood Shores Parkway, Suite 240Redwood City, California

Principal AuthorRobert Reitherman

Contributing Author Sue C. Perry

Project ManagerTh omas R. McLane

Project Review PanelRonald P. Gallagher

Jon A. HeintzWilliam T. Holmes

Ugo MorelliLawrence D. ReaveleyChristopher Rojahn

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Any opinions, fi ndings, conclusions, or recom-mendations expressed in this publication do not necessarily refl ect the views of FEMA. Additionally, neither FEMA or any of its employees makes any warrantee, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, product, or process included in this publication. Users of information from this publication assume all liability arising from such use.

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1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Unreinforced Masonry Buildings and Earthquakes: Where in the

United States are the Risks? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Types of Earthquake Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Earthquake Performance of Unreinforced Masonry Buildings . . . . . . . 7What is Unreinforced Masonry? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Examples and Statistics from Past U.S. Earthquakes . . . . . . . . . . . . . . . . . . 10

3 Developing a Strategy for Implementing a URM Building Risk Reduction Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Occupancy and Ownership Factors: Th e People Who Own and Use the Buildings . 16Historic and Architectural Character . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Cost Issues Related to Seismic Retrofi ts . . . . . . . . . . . . . . . . . . . . . . . . . 17City Planning Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4 Examples of Successful Risk Reduction Programs . . . . . . . . . . . . . . 19Compiling an Inventory of Unreinforced Masonry Buildings . . . . . . . . . . . . . 19Successful Programs Require Sustained Support and Leadership . . . . . . . . . . . 20Utah: Engineering Inspections Triggered by Re-roofi ng Projects . . . . . . . . . . . 20Utah: Statewide Inventory of Unreinforced Masonry Buildings . . . . . . . . . . . . 21State of California Unreinforced Masonry Building Law: Measuring

the Problem and the Progress Toward Addressing It . . . . . . . . . . . . . . . 22Seattle, Washington: Saving Historic Buildings . . . . . . . . . . . . . . . . . . . . . 23Seattle, Washington: Combining Modernization with Seismic Retrofi tting . . . . . 23Oregon: A Statewide Inventory and Funding Approach for Schools and

Essential Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Berkeley and Other California Cities: Financial Incentives for Retrofi tting . . . . . 24Public Schools in California: A Statewide Approach to a Special Kind of Facility . . 25Long Beach, California: A Pioneering Accomplishment. . . . . . . . . . . . . . . . . 25Los Angeles, California: Evidence of the Eff ectiveness of Retrofi ts . . . . . . . . . . 26San Luis Obispo, California: Making the Eff ort to Communicate with

Building Owners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5 Additional Technical Background on Unreinforced Masonry Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29How Do Unreinforced Masonry Buildings Behave in Earthquakes?. . . . . . . . . . 31How Are Unreinforced Masonry Buildings Seismically Retrofi tted? . . . . . . . . . 34

6 Sources of Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Publications for the General Public . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Historic Buildings and Seismic Retrofi ts . . . . . . . . . . . . . . . . . . . . . . . . . 40Building Inventories and Evaluation of Existing Buildings . . . . . . . . . . . . . . . 40Building Codes, Standards, Guidelines, and Laws Applicable to Existing Buildings. 41Costs of Seismic Retrofi ts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

7 End Notes and Cited References . . . . . . . . . . . . . . . . . . . . . . . . . 43

8 Project Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 1

1 Introduction

This document provides guidance on how to develop programs to reduce the earthquake risks of existing unreinforced masonry buildings. As the fol-

lowing chapters will show, this building type is typically the most seismically vulnerable category of construction in a community, and it is by far the most common type of building to be singled out for voluntary or mandatory seismic risk reduction programs in the United States.

While the information presented here is based on extensive earthquake engineer-ing knowledge, this guide has been written for use by a non-technical audience, including government offi cials, building owners, and the general public. It also contains relevant information for building offi cials, consulting structural engi-neers and building contractors.

Unreinforced masonry walls do not have a grid of steel

reinforcing bars embedded within them. See Chapters 2 and 5 for further description.

Th e typical unreinforced masonry building in the United States has brick walls with no steel reinforcing bars embedded within them. A more precise defi nition of unreinforced masonry buildings or “URMs,” as they are known in many places, is contained in Chapter 2, “Earthquake Perfomance of

Unreinforced Masonry Buildings.” Additional details about their construction are included in Chapter 5. Th e reader does not need to study all of this terminology, but he or she should clearly understand the basic diff erences between unreinforced and reinforced masonry.

Chapter 3, “Developing a Strategy for Implementing a URM Risk Reduction Program,” describes how a number of factors unrelated to construction are involved in any eff orts to reduce unreinforced masonry seismic risks. Th ose factors include retrofi t costs and the economic viability of older existing buildings, the number of occupants and type of use of the buildings, and the historic or architec-tural character of the buildings. Each of these considerations involves an impor-tant segment of the community that should be included in active consideration of any risk reduction program.

Th is guide does not presume to prescribe a rigidly uniform sequence of steps that must be taken in order to reduce risk. As Chapter 4, “Examples of Successful Risk Reduction Programs,” clearly documents, a wide variety of approaches has been developed across the country.

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2 Introduction

Chapter 5, “Additional Technical Background on Unreinforced Masonry Buildings,” provides simple explanations of some key earthquake engineering terminology and concepts for the non-engineer audience. Th is information is intended to help facilitate conversations between the non-technical audience, such as city offi cials and the general public, and the technical community that includes building inspec-tors, engineers, and architects.

Chapter 6, “Sources of Information,” provides a number of annotated references for both technical (engineering-oriented) and non-technical audiences.

Chapter 7, “End Notes and Cited References,” provides notes and cites references to document all of the information presented in this guide. Almost all of the Sources of Information and the Cited References are accessible on the internet free of charge.

Unreinforced Masonry Buildings and Earthquakes: Where in the United States are the Risks?

If the current building code in a locale does not

allow unreinforced masonry construction, then existing buildings of that type can be considered a signifi cant earthquake risk that should be investigated further.

Current U.S. building codes (described further in Chapter 2) allow unreinforced masonry walls in new building construction only in those areas where the probability or chance of strong earthquake shaking is very low. In past decades, however, many thousands of unrein-forced masonry buildings were constructed in all areas of the country, even in regions subject to the most frequent strong earthquakes. In the light of today’s knowledge, we recognize

that this existing URM building stock presents a problem with respect to earth-quake risk.

Th e URM problem in jurisdictions that are now eff ectively enforcing the current building code (essentially the latest edition of the International Building Code, the IBC) is due to those buildings that were built before recent model code seismic pro-visions were adopted and enforced. Th e jurisdiction’s building department can pro-vide the benchmark date, when the locally enforced building code began to include seismic provisions that cover unreinforced masonry. Unreinforced masonry build-ings can be found in every state. Because of its durability, fi re resistance, and archi-tectural character, unreinforced masonry has often been the construction material of choice for schools, city halls, central business district buildings, factories, and apartment buildings. However, the probability of strong earthquake shaking is not equally distributed across the states, which raises the question: Where in the United States are unreinforced masonry buildings of concern?

Figure 1 provides a general view of those areas of the U.S. where unreinforced masonry is not permitted for current construction.1 Th is Figure serves as an initial guide to where some level of concern is warranted regarding the earthquake risks posed by these buildings. A local building department or a consulting structural engineer can provide more detailed guidance as to whether current seismic code provisions allow unreinforced masonry for a precise location, type of soil, and occupancy or use of a building. Even in regions where unreinforced masonry is cur-rently allowed, older unreinforced masonry buildings may exist in a deteriorated

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 3

Figure 1. Approximate mapping of the areas of the United States where current building code regulations do not allow new construction with unreinforced masonry.

state much weaker than that required by code today. Assessing the earthquake vulnerabilities of older unreinforced masonry buildings appropriately in areas that still allow URM construction might take the form of requiring inspection of exterior materials, especially masonry materials like bricks or terra cotta, in order to ensure they are still attached fi rmly enough to prevent falling. Chicago, for example, has passed a local building condition assessment ordinance that requires periodic inspection of building facades, although the city is located in an area where the current International Building Code allows unreinforced masonry.

Types of Earthquake Risks

Poor building performance poses three basic types of risk in an earthquake: the risk of injury, property damage, and loss of use. Spending the time and eff ort, and imposing the new regulations and costs on building owners, to implement a risk reduction program for unreinforced masonry buildings makes sense when it is clearly based on reducing one or more of these types of risk.

INJURY: Promoting safety is the prime rationale for building code regulations in general, whether applied to earthquakes, fi res, or other hazards. Damage to unreinforced masonry buildings is dangerous. When masonry debris falls, it is potentially lethal. A single brick

weighs from 6 to 12 pounds (2½ to 5 kg), and just one square foot of a typical wall weighs 120 pounds or more (over 50 kg). Unreinforced masonry buildings are dangerous not only to their occupants but also to those in adjacent buildings and to pedestrians. Figure 2 illustrates the danger of falling masonry debris, even if the entire building does not collapse. Parapets, which are the short walls that often extend around the perimeter of a roof (as in the two buildings pictured in Figure 2), are particularly vulnerable, as are chimneys and cornices (the decorative ledges that run around the top of the building). Figure 3 illustrates the level of danger posed by complete collapse of a URM building.

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4 Introduction

PROPERTY DAMAGE: Experience from past earthquakes has shown that expensive repairs will be needed to an unreinforced masonry building, after an earthquake. More than for any other kind of dam-aged building, there is often no way to “put Humpty Dumpty back

together again” for a URM building. Th is results in the demolition of the building. Some of the most architecturally prominent and historically valued buildings in the United States are made of unreinforced masonry. See Figure 4. Protecting these architectural and historic assets may be an important goal of risk reduction programs, in addition to preventing costly damage. Th e damage to the Pacifi c Avenue Historic District in the city of Santa Cruz that resulted from the 1989 Loma Prieta earthquake was so extensive that the downtown area was removed from the National Register of Historic Places (see Figure 5). In that Historic District, 52% of the old brick buildings were so badly damaged that they were quickly demolished, and another 16% were “red-tagged” (closed because they were unsafe to enter2).

LOSS OF USE: Even minor earthquake damage can require the closure of an unreinforced masonry building, until repairs are made. More often than for other kinds of construction, a damaged unreinforced masonry building may need to be upgraded to a higher level of safety

than it possessed in its pre-earthquake state, before it can reopen. Closure of a building, while permits are obtained and a major re-construction project is carried out, often lasts for several years. Th e kind of damage shown in Figure 6, which causes the building to be “red tagged” as unsafe to enter, can present so many problems in bringing the building back into use that long-term vacancy or demoli-tion of the building may result.

Figure 2. Diagram illustrating the dangers of unre-inforced masonry. When unreinforced masonry buildings begin to come apart in earthquakes, heavy debris can fall on adjacent buildings or onto the exterior where pedestrians are located. This diagram illustrates the failure of parapets, one of the most common types of unreinforced masonry building damage. This level of damage can occur even in relatively light earthquake shaking. —Rutherford & Chekene

Figure 3. Complete collapse of an unreinforced brick building. The most severe level of damage, with the greatest likelihood of fatalities, is complete collapse. After a few seconds of ground shaking in the 1933 Long Beach earthquake, the brick walls holding up the second fl oor and roof of this building broke apart. That not only caused the fall of hazardous brick debris—it also immediately led to complete collapse. —Los Angeles Public Library

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 5

Figure 4. The Salt Lake City and County Building, an architectural and historic community asset that could be lost, if damaged.The Salt Lake City and County Building was extensively seismically retrofi tted, not only to make it safer but also to provide long-term protection for a valued his-toric building. —U.S. Geological Survey

Figure 5. Destruction of a historic building.Complete collapse of one of the historic buildings in the former Pacifi c Avenue Historic District of the City of Santa Cruz, California. —James R. Blacklock, NISEE, U.C. Berkeley

Figure 6. Damaged URM wall in a red-tagged building, fated to be torn down or to undergo a multi-year clo-sure for repairs and upgrading.Pre-earthquake retrofi tting usually looks quite modest, compared to the comprehensive upgrading that building codes will require to repair a damaged, non-code-conforming building after an earthquake. —Robert Reitherman

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6 Introduction

All three kinds of risk—injury, property damage, and loss of use—are usually greater for unreinforced masonry buildings than for the other buildings in a city or region. While some communities, university systems, owners, and others have cho-sen to deal with the risks of other kinds of existing buildings or to upgrade utility and transportation systems,3 addressing unreinforced masonry building problems is usually the top priority in any serious eff ort to provide seismic protection.

Dealing with the earthquake risks of unreinforced masonry buildings is a challeng-ing and diffi cult undertaking. However, many communities have developed success-ful risk reduction strategies. A number of examples are presented in Chapter 4.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 7

2 Earthquake Performance of Unreinforced Masonry Buildings

This chapter provides brief descriptions and illustrations of unreinforced masonry, along with explanations of why unreinforced masonry buildings

are so susceptible to earthquake damage. When subjected to strong earth-quake shaking in past U.S. earthquakes, fi ve out of six URM buildings have been damaged to the extent that potentially lethal amounts of brickwork fell. One-fi fth of those buildings either partially or completely collapsed.4

What is Unreinforced Masonry?

Unreinforced masonry can be defi ned generally as masonry that contains no rein-forcing in it. Th e terms “unreinforced” and “masonry” are both more precisely described in this chapter. A shared understanding of these facts and defi nitions will be helpful to conversations between engineers and non-engineers, when discussing a risk reduction program.

Masonry is made of earthen materials and includes the sub-types listed below. Th e most common unreinforced masonry materials used for the walls of buildings are the fi rst two listed, brick and hollow concrete block, which are illustrated in Figure 7, Figure 8, and Figure 9.

• Brick: clay that is fi red to a hard consistency.

• Hollow concrete block: “concrete masonry unit” in the terminology of building codes, commonly known as “cinder block.”

• Hollow clay tile: similar to concrete block in shape, having hollow cells, but brick-colored.

• Stone: can be “dressed” or cut into rectangular blocks, or used in its natural shape.

• Adobe: mud poured into the form of walls or made into sun-dried bricks.

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8 Earthquake Performance of Unreinforced Masonry Buildings

Bearing walls perform the essential job of

resisting gravity and holding a building up. Destruction of bearing walls leads to collapse.

Th e most common type of unreinforced masonry building in the United States is constructed of brick walls, with wood-frame fl oors and roof, as shown in Figure 10 and Figure 11. From the outside, one can observe that the spans over windows are short, and the walls are thick. Th e masonry walls around the exterior, and sometimes similar walls in the inte-rior, bear up under the weight that is delivered to

them by fl oor or roof beams. For this reason, they are called bearing walls. When the masonry is built into the rectangular openings or bays of a concrete or steel frame, with the frame holding up the masonry, then they are called infi ll walls. Th at kind of building requires its own special analysis and is not in the subject of this booklet.

Figure 8. “Header” versus “stretcher” courses.The presence of header courses is usually the easiest way to tell if a brick wall is unreinforced.

Figure 9. Complete collapse of an unrein-forced concrete block building, 1971 San Fernando earthquake. —Karl Steinbrugge, NISEE, U.C. Berkeley

Unreinforced concrete block walls do not have reinforcing steel bars placed vertically in the hollow cells or horizontally between the courses.

Figure 7. Components of unreinforced brick (left) and unreinforced concrete block (right) walls.

Header bricks extend into the wall, indicating that there is no cavity where reinforcing could have been placed.

Wythe (2-wythe-thick wall shown)

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 9

Masonry veneer is usually composed of one layer of ordinary brick or of thinner brick that is applied to a supporting wall behind it, as shown in Figure 12. Veneer is typically about four inches (100 mm) or less in thickness. It may also consist of stone facing. Th e veneer is adhered to and literally hangs onto a wall behind it for vertical and horizontal support. Terra cotta, a ceramic material similar to brick

Figure 12. Workers installing brick veneer.The individual pieces of veneer are being adhered to the reinforced concrete wall behind them. The result looks like a brick wall. —Robert Reitherman

Figure 10. Typical appearance of a multistory unreinforced brick building.When buildings are much taller than this, there is often also a steel or concrete frame, making an infi ll struc-ture. —Rutherford and Chekene

Figure 11. Components of a URM building. Many larger unreinforced brick buildings have heavy timber columns and beams in the interior. The wooden posts and beams do not provide signifi cant horizontal (earthquake) force resistance. —FEMA 154, Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook

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10 Earthquake Performance of Unreinforced Masonry Buildings

that has a smooth fi nish and is made in various forms and colors, was often used in older buildings for both decorations and veneer. Current code provisions in areas of seismic activity include requirements to prevent veneer from falling off in an earthquake. Older buildings with thick (one-brick thick) veneer that does not meet current seismic safety requirements can experience the veneer peeling off , when the building is shaken. Masonry veneer on houses is typically more of a prop-erty damage risk than a signifi cant safety risk. However, veneer on taller walls in public settings adjacent to areas where pedestrians may be presents a signifi cant risk that an unreinforced masonry risk reduction program should consider.

Further information on unreinforced masonry construction is provided in Chapter 5.

Examples and Statistics from Past U.S. Earthquakes

A number of earthquakes in the United States would have resulted in some prop-erty loss but no real disaster, if damage to unreinforced masonry buildings had not occurred. Th e following brief survey provides evidence in support of this conclu-sion. Magnitude (M) numbers are included for each earthquake below. While one may often hear references to the “Richter scale,” in many cases today, seismologists measure the overall size of an earthquake using one of the other magnitude scales that were developed after Charles Richter developed his in 1935. Th e diff erences in magnitude scales are not particularly relevant here. Th e symbol M below stands for generic earthquake magnitude.

1886 Charleston Earthquake, South Carolina, M 7.7: Eighty-two percent of the brick buildings suff ered more than minor damage, and 7% collapsed or were demolished.5 See Figure 13, illustrating the debris from collapsing second story masonry walls, which extends beyond the middle of the street.

Figure 13. Debris result-ing from the 1886 Charleston, South Carolina earthquake. —NISEE, U.C. Berkeley

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 11

1925 Santa Barbara Earthquake, Southern California, M 6.2: Th e most severe damage from this earthquake occurred among unreinforced brick com-mercial and residential construction and was a primary motivation for engineers in California to adapt seismic design ideas from Japan into the Uniform Building Code. Forty percent of the unreinforced masonry buildings were severely damaged or collapsed.6 See Figure 14, the Hotel Californian, in which extensive wood-frame and plaster partitions barely managed to hold the building up, after exterior brick walls failed.

Figure 14. Heavily damaged Hotel Californian, 1925 Santa Barbara, California earthquake. —NISEE, U.C. Berkeley

1933 Long Beach Earthquake, Southern California, M 6.3: In the City of Long Beach (adjacent to the City of Los Angeles), 54% of the unreinforced masonry buildings ended up with damage that ranged from signifi cant wall destruction to complete collapse. In 20% of the cases, damage fell in the categories of either damage to more than half the wall area, partial collapse, or complete collapse.7 See Figure 15, showing parapet (the short walls that often extend around the perim-eter of a roof) and top story failure and the eff ect of the falling masonry debris.

Figure 15. URM building damage, 1933 Long Beach, California earth-quake. —Los Angeles County Public Library

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12 Earthquake Performance of Unreinforced Masonry Buildings

1983 Coalinga Earthquake, Central California, M 6.2: Out of 37 unrein-forced masonry buildings—the core of the Coalinga business district—only one escaped damage. Sixty percent were damaged to the extent of having more than half of their walls ruined, up to complete collapse.8 Th e entire downtown area was cordoned off , until badly damaged buildings could be demolished and the debris removed. See Figure 16, which illustrates a common form of damage, in which the gable (peaked roof) end wall falls.

Figure 16. URM building with end-wall failure, 1983 Coalinga, California earth-quake. Robert Reitherman —NISEE, U.C. Berkeley

1983 Borah Peak Earthquake, Idaho, M 7.3: In the town of Challis, Idaho, the only earthquake-related fatalities occurred when an unreinforced masonry wall fell on two children on their way to school. In Mackay, the town’s main street build-ings, built of unreinforced brick, concrete block, or stone, were all damaged, Eight required demolition. In relative terms, when compared to the size of the town (see Figure 17), this amount of damage constituted a large disaster.

Figure 17. Aerial view of heavily dam-aged Mackay, Idaho. The unreinforced masonry buildings on the main commercial street of the small town were badly damaged in the 1983 Borah Peak, Idaho earthquake. —NISEE, U.C.Berkeley

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 13

1989 Loma Prieta Earthquake, Northern California, M 7.1: In this earth-quake, 374 (16%) of the 2,400 unreinforced masonry buildings in the region expe-rienced damage severe enough to require that they be vacated.9 Th e earthquake was centered 60 miles south of the San Francisco Bay Area, and the majority of these buildings were subjected to only light to moderate shaking. Figure 18 illus-trates an upper-story failure of brickwork, which fell onto the sidewalk and cars below, killing fi ve people.

Figure 18. Upper story wall collapse, with resulting fatalities. Five people were killed when the brick wall in the fourth story fell on top of cars and the sidewalk in the 1989 Loma Prieta earthquake. —James Blacklock, NISEE, U.C. Berkeley

2001 Nisqually Earthquake, Puget Sound Region, Washington, M 6.8: “URM buildings built before 1950 exhibited the poorest behavior. Th e most com-mon damage included shedding of brick from parapets and chimneys. Other URM buildings exhibited diagonal ‘stair-step’ cracking in walls and piers, damage to walls in the upper stories, vertical cracking in walls, damage to masonry arches, and damage to walls as a result of pounding. In many cases, fallen brick resulted in damage to objects, such as cars and canopies, outside the building.”10 See Figure 19.

Figure 19. URM building damage, 2001 Nisqually, Washington earthquake. At left, hollow clay tile debris from a collapsed wall; at right, diagonal “stair-step” crack-ing of a brick wall (the crack following mortar horizontal bed joint and vertical head joint lines), a sign of the wall’s inability to resist shear stress from in-plane forces. —André Filiatraut

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14 Earthquake Performance of Unreinforced Masonry Buildings

2003 San Simeon Earthquake, Central California, M 6.5: Of 53 unreinforced masonry buildings in Paso Robles, the nearest aff ected city, none of the nine that had been retrofi tted experienced major damage. Many of the others were damaged so extensively that they were subsequently demolished. “During earthquakes unre-inforced masonry buildings that have not been retrofi tted continue to be the most dangerous buildings in California.” One building owner commented afterward: “I’m confi dent the building would have come down in the quake if we hadn’t done the retrofi tting. Th ere were times when we were bleeding so badly in paying for it, we wondered what in the heck we were doing. Now we know.”11 See Figure 20. Th e two fatalities in the town were due to the collapse of an unretrofi tted, unreinforced brick building.

Figure 20. Retrofi tted URM building, 2003 San Simeon, California earthquake. Retrofi tted prior to the earthquake, this unre-inforced brick building experienced no damage. —Janise E. Rodgers, NISEE, U.C. Berkeley.

Putting together the statistics on 4,457 unreinforced masonry buildings from sev-eral U.S. earthquakes4, we see the following profi le of how unreinforced masonry buildings perform, when strong earthquake shaking occurs:

• Five out of six are damaged enough for brickwork to fall;

• One-fi fth are damaged to the point of partial or complete collapse.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 15

3 Developing a Strategy for Implementing a URM Building Risk Reduction Program

A number of considerations should be taken into account when developing a strategy for implementing an unreinforced masonry building risk reduction

program. Each consideration involves key individuals and groups who will formu-late, carry out, and be affected by the program. For that reason, it is important to involve them as early in the process as possible.

Many considerations must be taken into account when developing a program to reduce the earthquake risks of unreinforced masonry buildings. Each consideration involves key individuals and groups, who should become involved at an early stage in the development process. For example, a planning department maintains informa-tion on the inhabitants and people who use the buildings in a community. Th e local building department is the agency that maintains data on the construction char-acteristics of buildings. Th is department is centrally involved in enforcing building code ordinances or voluntary construction standards and in issuing permits for any retrofi t construction projects. Economic factors in a risk reduction program obvi-ously aff ect building owners (and retrofi t costs often “fl ow down” to tenants); in addition, fi nancial and real estate institutions may have relevant insights and inter-ests regarding the program. Agencies or non-profi t organizations with architectural or historical preservation interests have a stake in how buildings of that character may be changed by any seismic retrofi ts. Finally, when unreinforced masonry build-ings are clustered together, as they often are in older central business districts, then risk reduction programs raise city planning issues with regard to zoning, parking, redevelopment eff orts, and other city concerns.

Retrofi tting is the process of

adding earthquake resistance to an existing building. It is generally synony-mous with the terms ‘seismic strength-ening’ or ‘seismic rehabilitation.’

Th e principal means of reducing the seismic risks of unreinforced masonry buildings is retrofi tting, although changing a building’s use in order to reduce its occupant load (number of occupants) also reduces risk. Retrofi tting an unreinforced masonry building can take several diff erent forms (see Chapter 5), but it must be kept in mind that a retrofi t is a signifi cant construction project, which may aff ect owners, occupants, and the community at large.

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16 Developing a Strategy for Implementing a URM Building Risk Reduction Program

Occupancy and Ownership Factors: The People Who Own and Use the Buildings

Th e usage or occupancy of a building is an important consideration, when planning a risk reduction program. Occupancies are defi ned by building codes in terms of the number of people who occupy a building and what the building’s functions are. More intensive uses, which bring more people to a building, increase risk exposure to earthquake-caused injuries. Current building code regulations require that essen-tial facilities such as fi re stations be designed to higher earthquake safety standards than ordinary buildings. Th is suggests that existing buildings with many occupants or essential facilities should have a higher priority for retrofi ts. Ownership patterns are also important. Twenty buildings on a school or college campus have one owner and ultimately, one decision-making process (for example, the setting of policies by a school board). Twenty buildings along a commercial street may be owned by twenty diff erent owners, with twenty distinct sets of decision-making variables involved, leading to greater variety of outcomes.

A retrofi t project in an apartment building that displaces residents for weeks or months presents the problem of where those residents will fi nd temporary housing. Are apartment buildings providing low-rent housing, so that passing along retrofi t costs to tenants in the form of higher rents will be a major economic burden? Are unreinforced masonry buildings located where few residents speak English? Such demographic factors must be taken into account, when planning how to craft a risk reduction program and how to involve the public. In San Francisco, a study was con-ducted to lay the groundwork for San Francisco’s unreinforced masonry building retrofi t program that specifi cally estimated what kinds of retrofi ts would be needed for residential buildings.

Historic and Architectural Character

Protecting people from the earthquake dangers of unreinforced masonry buildings must be a community’s highest priority. However, protecting the property value of buildings by preventing damage is also important. In addition, some buildings have historic or architectural signifi cance, which is itself a value to be preserved. Because masonry is a durable material and was often the fi rst choice for important build-ings constructed in the past, many communities’ most historic and architecturally valued buildings are of this structural type, as in the case illustrated in Figure 21.

Retrofi tting these buildings to increase their earthquake resistance is necessary in order to prevent irreparable damage from occurring to the buildings in an earth-quake. Yet the retrofi t itself can alter the building’s appearance and change its his-toric materials in an undesirable way, if not carried out sensitively. Fortunately, today’s earthquake engineering methods provide options for dealing with the earth-quake vulnerabilities of a building, while leaving its appearance largely unchanged. As Chapter 5 discusses, the technique of seismic isolation has been used for some monumental public buildings with extensive unreinforced masonry components. Th ese isolators can reduce the seismic forces on the building to only one third of what they would otherwise be, and the isolators are usually installed unobtrusively at the foundation or basement level.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 17

Cost Issues Related to Seismic Retrofi ts

Groups like a downtown business owners association or chamber of commerce, an apartment owners or renters association, or a historic preservation league, may have concerns about retrofi t costs. Structurally strengthening an unreinforced masonry building is not an inexpensive remodeling project, and the cost implica-tions must be considered. As part of developing a risk reduction plan, it is impor-tant to collect information on the economic viability of the unreinforced masonry buildings at issue. Are the buildings high in value, generating strong income streams, because they form the heart of the “old town” tourist district that is com-mon in many cities? Or are they in a declining area that used to be the central busi-ness district but which has been supplanted by shopping centers and offi ce parks located elsewhere? Do the properties provide enough collateral for their owners to obtain construction loans to fi nance the upgrading work?

FEMA provides an on-line retrofi t cost estimating feature on its website,12 and FEMA documents provide further information.13 Costs can vary greatly, however, so locally-based estimates should be carried out prior to instituting a risk reduc-tion program.

City Planning Factors

An inventory of unreinforced masonry buildings can be presented in table format, to display the buildings’ square footage and number of stories, construction dates, and occupancy. Building location is also signifi cant. Are buildings dispersed throughout an area, or are they clustered? How are they located with respect to current zoning districts? Th e community may have a long-range plan for streets, parking, plazas and pedestrian areas. Any economic redevelopment plans should include a list of the locations of unreinforced masonry buildings. Aside from an individual building’s architectural or historic merits, it is important to consider the collective eff ect for a town or city of having a number of well-preserved, economically vital, older build-ings that defi ne the overall community character. Th ere may also be environmental

Figure 21. Pioneer Square Historic District, Seattle, Washington. The historic buildings in this city district are unreinforced masonry buildings. This is often the case.


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18 Developing a Strategy for Implementing a URM Building Risk Reduction Program

impact reporting requirements that a retrofi t program would trigger; city planning departments should be familiar with any such requirements. Figure 22 illustrates how an inventory of unreinforced masonry buildings can be overlaid with political and economic (building value) data.

As the examples in Chapter 4 make clear, a variety of risk reduction approaches that address these factors have been successfully adopted. Developing these successful approaches has almost always required involving the key individuals and groups associated with each consideration in the planning and decision-making process.

Figure 22. The distribu-tion of unreinforced masonry buildings in the greater New York City region. Maps such as this one, published by the New York City Area Consortium for Earthquake Loss Mitigation, relate seismic information to geographic and land use plan-ning data.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 19

Rapid Visual Screening of Buildings for Potential Seismic Hazards FEMA-154 Data Collection Form HIGH Seismicity

Address: __________________________________________________

_________________________________Zip _______________

Other Identifiers _____________________________________________

No. Stories ________________________________ Year Built ________

Screener _____________________________ Date _________________

Total Floor Area (sq. ft.) _______________________________________

Building Name ______________________________________________

Use _______________________________________________________



Assembly Govt. Office Commercial Historic Residential Emer. Services Industrial School

Number of Persons 0 – 10 11 – 100 101-1000 1000+

A B C D E F Hard Avg. Dense Stiff Soft Poor Rock Rock Soil Soil Soil Soil

Unreinforced Parapets Cladding Other: Chimneys _____________



S2 (BR)

S3 (LM)

S4 (RC SW)


C1 (MRF)

C2 (SW)


PC1 (TU)

PC2 RM1 (FD)

RM2 (RD)


Basic Score

Mid Rise (4 to 7 stories)

High Rise (> 7 stories)

Vertical Irregularity





























































































Soil Type C

Soil Type D

Soil Type E
















































Detailed Evaluation Required


* = Estimated, subjective, or unreliable data DNK = Do Not Know

Plan Irregularity -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5

BR = Braced frameFD = Flexible diaphragmLM = Light metal

MRF = Moment-resisting frameRC = Reinforced concreteRD = Rigid diaphragm

SW = Shear wallTU = Tilt upURM INF = Unreinforced masonry infill


4 Examples of Successful Risk Reduction Programs

A large number of unreinforced masonry building risk reduction programs have been implemented across the United States. A sample of representative pro-

grams is included here, to illustrate the variety of possible approaches.

“If the shoe doesn’t fi t, then don’t wear it” is a good caveat to add, when giving advice. While one of the following programs may provide an ideal model for a given community, it is likely that a new risk reduction program will require some unique features based on the particular situation in that community. Th e examples presented in this chapter illustrate key components of risk reduction programs, which communities can then synthesize in a variety of ways, in order to suit their particular circumstances.

Compiling an Inventory of Unreinforced Masonry Buildings

Most programs to reduce unreinforced masonry seismic risks share certain charac-teristics. First, they all need to include an inventory of buildings, which should be carried out early in the planning process. Conducting an inventory is not diffi cult, because unreinforced masonry buildings are among the easiest of construction types to identify. Building department, insurance industry, and tax assessor fi les can sometimes provide useful information. “Sidewalk surveys” that observe build-ings from the outside are often suffi cient. Th e FEMA 154 Handbook provides a “rapid visual screening” method that is applicable to a wide variety of buildings14 (see Figure 23). Section E.13 of Appendix E of the FEMA 154 Handbook provides



AssembCommeEmer. S


Basic Sc

Mid Rise

High Ris


Pre Cod

Plan Irre

Figure 23. FEMA 154, a technical resource containing forms and standard-ized guidance on compiling an inven-tory. —FEMA 154, Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook

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20 Examples of Successful Risk Reduction Programs

relevant information for a screening program restricted to unreinforced masonry buildings. Any inventory needs to include not only the overall quantity of unrein-forced masonry buildings, but also their locations, ownership and physical charac-teristics, as well as social or city planning factors. Typically, a building department and planning department of the jurisdiction are key actors in carrying out that inventory. Local structural engineers and architects can also be a valuable source of expertise and knowledge.

Successful Programs Require Sustained Support and Leadership

More broadly, successful programs share another trait: they benefi t from the sus-tained support and eff orts of individuals and organizations that recognize the value of earthquake protection and are willing to work for it. Th e following conclusion, from a review of successful seismic safety programs in the United States,15 out-lines concisely some of the challenges that arise when addressing the unreinforced masonry building problem (Note: interested readers can fi nd more information on social aspects of seismic safety eff orts in the references cited in the passage below):

Promoting seismic safety is diffi cult. Earthquakes are not high on the political agenda because they occur infrequently and are overshadowed by more immediate, visible issues. Even where citizens are aware of seismic risks, taking action to improve seismic safety is diffi cult because costs are immediate and benefi ts uncertain, public safety is not visible, benefi ts may not occur during the tenure of current elected offi cials, and seismic safety lacks a signifi cant public constituency (Olshansky and Kartez, 1998; Lambright, 1984; May, 1991; Drabek et al., 1983; Rossi et al., 1982; Wyner and Mann, 1986; Alesch and Petak, 1986; Berke and Beatley, 1992). Many factors are critical to the successful advancement of seismic safety at local and state levels. Th ese include public advancement of the problem; persistent, skillful, and credible advocates; repeated interaction and communication among participants; availability of staff resources; linkage to other issues; occurrence of a disaster that leads to a ‘‘window of opportunity’’ for change; community wealth and resources; assistance from higher levels of government; and previous experience with hazards (Berke and Beatley, 1992; Olshansky and Kartez, 1998). Of these, advocacy stands out because it represents a way that individuals can make a diff erence. 15

Utah: Engineering Inspections Triggered by Re-roofi ng Projects

This program, implemented in a variety of ways by

local governments across Utah, has the virtue of setting a deadline almost automatically.

Th e Utah Uniform Building Standard Act Rules have been amended to add a way to upgrade the earthquake resistance and general struc-tural safety of buildings, especially unrein-forced masonry ones, incrementally. When embarking on a re-roofi ng project, the building owner must retain an engineer to inspect the

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 21

adequacy of the building’s roof-to-wall connections and the ability of its parapet walls and cornices to withstand horizontal earthquake forces. Th e logic behind this incremental approach is that the removal of old roofi ng presents an opportune time for an engineer to inspect these conditions, and that any strengthening measures would be carried out prior to re-roofi ng, as part of that construction project. Section R156-56-801, Statewide Amendments to the IBC (International Building Code), Section 58, requires that these appendages be able to withstand 75% of the force levels that are stipulated for new buildings. Portions of the building that don’t perform up to that standard must be either reinforced or removed. Buildings built after 1975, when codes for new buildings began to address this seismic vulnerability in Utah, are exempt.16

Roofi ng materials will typically need to be replaced within a time period of twenty to forty years, and that replacement work will then trigger this retroactive seismic requirement. It is common for building codes to require retroactive upgrading of safety features, if a building is to be signifi cantly remodeled. Th e reasoning is that the remodel will extend the life of the building and that in the context of a major renovation project, the safety improvements will represent only a minor cost.

Utah: Statewide Inventory of Unreinforced Masonry Buildings

The evolving Utah program demonstrates the need

to conduct an inventory of buildings as a fi rst step in evaluating their seismic risks and the costs and methods that could best be used to retrofi t them.

In 2008, the Utah legislature passed a resolu-tion urging “the Utah Seismic Safety Commission to compile an inventory of unreinforced masonry buildings so that the quantity and extent of the problem in Utah can be determined. Be it further resolved that the Legislature urges the Utah Seismic Safety Commission to recommend priorities to address the problem in a manner that will most eff ectively protect the lives, property,

and economy of the state.”17 Similar in some respects to the California case described below, the strategy here is fi rst, to identify the location and size of the problem and then, to devise appropriate solutions. Utah is unique among the most highly seismic states of the United States, in that it has many single-family dwellings of unreinforced masonry construction. Th ese smaller buildings present diff erent (usually lesser) risks of collapse or injury, but they also could have a very high impact on the population after an earthquake, if many such housing units were unsafe to occupy, and if homeowners’ investments in their homes were wiped out. In the Salt Lake Valley alone, there are over 185,000 unreinforced masonry buildings, many of them single-family residences, typically built with hollow walls that do not comply with model codes and retrofi t provisions such as the Uniform Code for Building Conservation.18

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22 Examples of Successful Risk Reduction Programs

State of California Unreinforced Masonry Building Law: Measuring the Problem and the Progress Toward Addressing It

The California program provides one example of a

state government imposing a basic requirement on local governments to identify their unreinforced masonry build-ings, while leaving open a range of ways in which they can deal with that risk.

In 1986, California passed a state law requir-ing all local governments situated in the highest seismicity zone of the currently enforced building code to inventory their unreinforced masonry buildings, to establish a risk reduction program, and to report results to the state. At that time, that highest zone of seismicity was Zone 4 of the Uniform Building Code, which was used in the West and Midwest, until the nationwide International Building Code took eff ect in 2000. Th e geo-

graphic scope of Zone 4 in California encompasses a population of approximately 28 million people. Th e state sought to balance its compelling interest in seismic safety against the cost of retrofi tting buildings by leaving its criteria for these new risk reduction programs loosely defi ned: a program could consist of as little as publishing a list of the unreinforced masonry buildings in a local jurisdiction and encouraging owners to renovate them, while posting warning signs at unretrofi t-ted buildings. Th us, a recent review of the law concluded, “On the surface, the level of compliance with this law has been quite high with over 98 percent of the 25,900 URM buildings now in loss reduction programs. But so far, only about 70 percent of the owners have reduced earthquake risk by retrofi tting in accordance with a recognized building code or by other means. Signifi cant progress has occurred, yet many URM programs are ineff ective in reducing future earthquake losses.”19 Relatively few of the 25,945 URM buildings addressed by the loss reduction programs were demolished. While demolition is sometimes desirable in order to renew the building stock, it is generally wise to minimize it to avoid abruptly changing the architectural and socio-economic fabric of a city.

Th e local programs with the strictest requirements require actual retrofi tting or demolition of the hazardous buildings. Next strictest are those programs that require owners to retain an engineer to produce an evaluation report, with actual retrofi tting remaining voluntary, perhaps encouraged by incentives. Th e California Seismic Safety Commission has found that voluntary strengthening programs have not been eff ective. One can conclude either that the incentives in voluntary programs have not been great enough, or that the absence of the “stick” to go along with the “carrot” is the weakness. Th e lowest level of compliance with the state law, and the least eff ective at reducing risks, is when local governments send a letter to the building owners informing them that the local building inventory conducted under state law found their building to be of unreinforced masonry construction. Th ese simple notices do not impose any requirement to have the building either evaluated by an engineer or upgraded. Th e Commission’s 2006 survey of local gov-ernments found that 52% had mandatory programs, 15% voluntary, 18% notifi ca-tion of owner only, with another 15% in a miscellaneous category. Th e Commission provides a suggested model ordinance. Once a local government makes that deci-sion and sets time tables, the actual engineering measures required are already set in model code provisions for existing buildings.20

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 23

Seattle, Washington: Saving Historic Buildings

This case illustrates the valuable support that an

organization knowledgeable about grants and loans can provide to retrofi t programs, by making funds available to bridge any funding gaps.

In the 2001 Nisqually earthquake, two-thirds of the 31 buildings that were posted as unsafe for occupancy (“red tagged”) were built of unrein-forced masonry, and many were a century old. “Historic” and “unreinforced masonry” are often synonymous. After that earthquake, Historic Seattle, a non-profi t advocacy organization, quickly launched a program of grants of approxi-mately $10,000 each to historic building owners:

the grants provided fi nancial support for initial engineering studies, with the goal being to have owners investigate repair and upgrading alternatives in lieu of demolition. While this initiative was a reaction to an earthquake rather than a preventive program in place prior to the earthquake, it still had the eff ect of promoting retrofi t measures to reduce earthquake risks from future earthquakes. In this case, those risks include both the risk of injury to occupants or pedestrians and the risk of irreparable damage to the buildings. Any Seattle resident who appreciates historic architecture will recognize many of the buildings that Historic Seattle helped through that program: Steil Building, McCoy’s Firehouse, Slugger Sports, Compass Center, Bread of Life Mission, Milwaukee Hotel and Alps Hotel, Hong Kong Building, Hip Sing Building, Panama Hotel, Bush Hotel, Bing Kung Building, Seattle Hebrew Academy, Trinity Parish Episcopal Church, Assay Offi ce, Mount Baker Park Presbyterian Church, and the Cadillac Hotel.21

Seattle, Washington: Combining Modernization with Seismic Retrofi tting

The voters who were asked to fund seismic

retrofi ts were supportive partly because the money was to be applied to essential facilities.

Th irty-two fi re stations in Seattle were identifi ed as needing modernization work that included energy conservation measures, general remodeling and in some cases, seismic upgrading. A ballot measure to approve a tax for that purpose was passed by a 69% majority of voters in 2003. Th e measure was introduced only two years after the Nisqually earthquake, when memories of damage

from that earthquake were fresh in the voters’ minds. Known as the Fire Facilities and Emergency Response Levy, the program integrates seismic retrofi ts with historic preservation requirements and with upgrading the stations to modern fi re safety and other standards. Th e $197 million in taxes average out to about $73 a year in additional property tax for the owner of a median-value house.22

Th is program provides more than one possible lesson for other local programs. Selecting an obviously high priority public safety category of facilities likely increased voter support, as did the recency of an earthquake (although a non-earthquake disaster might also be an impetus for multi-hazard upgrades). Rather than fi rst imposing requirements on private property owners, the local govern-ment also provided leadership by example, by dealing with vulnerabilities in its own buildings. And in packaging a variety of renovation measures along with seismic retrofi tting, more cost-eff ective construction projects resulted.

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24 Examples of Successful Risk Reduction Programs

Oregon: A Statewide Inventory and Funding Approach for Schools and Essential Facilities

This example illustrates the value of assembling

a committee or task force comprised of a variety of important community organizations.

In 2002, Oregon voters approved two seismic safety measures. One allowed the use of general obligation bonds to fi nance seismic upgrades of educational facilities owned by the State govern-ment (including State universities and community colleges) and local governments (local public school districts). A companion measure applied to fi re, police, and hospital buildings. Th e educa-

tional measure followed up on a state law passed by the legislature in 2001 that required seismic evaluations of schools, using a standardized method published by FEMA.23 While these laws launched Oregon on the path toward reducing seismic risks from existing buildings—URM buildings being prominent among them—no funding was provided to implement the initiatives. Th e Oregon Seismic Safety Policy Advisory Committee and the Division of Geology and Mineral Industries subsequently worked to obtain funding to conduct a statewide seismic evaluation of educational and emergency services buildings, and to put bonds on the ballot as needed to correct the seismic defi ciencies found.24

Berkeley and Other California Cities: Financial Incentives for Retrofi tting

A “carrot and stick” approach can be more

effective than using an incentive or penalty alone.

Because the City of Berkeley levies a tax of 1.5% of the selling price of real estate, it has the leverage to refund a portion of that tax, if the new owner carries out seismic retrofi t work. Th e City will refund retrofi t expenses up to one-third of that tax amount (up to 1/2% of the property value transferred) for qualifying residential

properties, when the new owner completes seismic retrofi t work within one year of purchase, up to a maximum refund of $2,000. While most of the properties included in the program have been wood-frame dwellings, unreinforced masonry buildings also qualify.25 In its fi rst decade of implementation, 12,000 properties were retrofi tted and rebates were issued totaling $6 million.

A number of other California cities off er incentives, and their programs are sum-marized by the Association of Bay Area Governments.26 Th ese programs include tax breaks, as in the Berkeley case; waiving of building permit fees for seismic upgrades; conferring zoning benefi ts such as an increase in density or exemption from non-conforming parking or other conditions; low-interest or no-interest fi nancing from publicly issued bonds or redevelopment district revenue, and; acquiring federal grant money for subsidizing retrofi ts. Th e Association of Bay Area Governments report includes information specifi c to unreinforced masonry buildings. A number of cities are included in that survey: Arroyo Grande, Berkeley, Fullerton, Inglewood, La Verne, Long Beach, Palo Alto, San Diego, San Jose, San Mateo, Sonoma, Torrance, Upland, Vacaville, and West Hollywood. Th e report also includes sample ordinances, state legislation, and other reference material.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 25

One possible lesson to be drawn from the examples of these cities is the value of off ering both a carrot and a stick, both incentives and requirements. As the California Seismic Safety Commission report19 noted, incentives by themselves have not led to signifi cant retrofi tting.

Public Schools in California: A Statewide Approach to a Special Kind of Facility

California legislation singled out schools as a high-priority

type of facility. The legislation set long-term but defi nitive dead-lines for retrofi tting buildings or taking them out of service.

Th e Long Beach earthquake in Southern California occurred at 5:54 p.m. on Friday, March 10, 1933. Th e fact that it barely missed occurring while children were in school and that the public saw numerous scenes of unreinforced masonry rubble on school campuses supplied graphic proof that new earthquake regulations in the

building code were needed. Prior to this time, there were no statewide earthquake regulations in the United States, and only a handful of California cities, such as Santa Barbara, which had gone through its own earthquake disaster in 1925, had any such provisions. Precisely one month after the Long Beach earthquake, the California legislature passed the Field Act, which eff ectively made the State into the building department for every school constructed by local governments (local school districts). Th e act prevented construction of new unreinforced masonry buildings and in 1939, the Garrison Act required school districts to inventory and to design a program for reducing the hazards of all pre-Field Act buildings. Th ese were essentially the unreinforced masonry buildings remaining on their campuses. However, this legislation did not lead to immediate retrofi t eff orts, and the law gave school board members immunity from liability, if they made an eff ort to secure funds for retrofi t eff orts via bond elections. One key reason for the lack of action was that there was no deadline in the Garrison Act. In 1967 and 1968, the legislature passed the Greene Acts. Th is action “put teeth” in the retroactive seismic safety requirements for schools by setting a 1970 deadline for producing structural evaluations of pre-1933 buildings and by prohibiting their use by students, as of 1975.27

Possible lessons for unreinforced masonry seismic safety programs include the singling out of a key public concern, such as safe schools, and the need to consider the possibility that deadlines and compliance may slip over time.

Long Beach, California: A Pioneering Accomplishment

The persistent and skillful efforts of just one person

can have a lasting effect.

Long Beach, California, where the 1933 earth-quake had been centered, was the fi rst city to enforce retroactive requirements to seismically upgrade unreinforced masonry buildings. In 1959, Edward O’Connor was the chief building

offi cial of the city, and he took upon himself the duty to identify the most hazard-ous of these buildings, including high-occupancy buildings like theaters, and to deliver the notice personally to the owners that they must either structurally

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26 Examples of Successful Risk Reduction Programs

strengthen them or tear them down. Th is case-by-case approach withstood resistance, based on a California Supreme Court case that justifi ed retroactive fi re safety requirements when high risk to public safety was present (retroactive “hazard abatement”). It later developed into a long-term, systematic law and program enacted and updated by the Long Beach City Council.28 Over time, as engineering developments occurred, technical details of the program evolved, but the essence of what one person began endured. By 1989, the unreinforced masonry buildings that had been rated as being in the most dangerous and intermediate dangerous categories had all been retrofi tted or demolished, although there remained 560 buildings in the third category of hazard.

In addition to the mandatory regulation, the city introduced an incentive by establishing an assessment district composed of the aff ected properties. Th e estab-lishment of the assessment district enabled the city to issue bonds, the proceeds of which would provide loans to the property owners and cover the city’s cost of implementing the fi nancial program and the building department’s monitoring of the retrofi t work. Th e repayment of the bonds came from assessments on the owners in the district. While owners paid the going rate for the loans, they would otherwise have been largely unavailable. Owners who defaulted on their loans could have their property foreclosed, with the city verifying in advance that there was enough value in the property to cover the loan value.29

Edward O’Connor had to go it alone, without other models of mandatory programs to refer to and without adopted engineering standards for the evaluation and ret-rofi t of unreinforced masonry buildings. Today, those resources are available. Still applicable as a lesson of this story, however, is the need for a dedicated lead indi-vidual to push steadily for the goal of seismic safety. It is also true that the local building department will usually be the key agency implementing such eff orts.

Los Angeles, California: Evidence of the Effectiveness of Retrofi ts

Successful local programs vary in their sources of

support, but three kinds are usually essential: a state or local structural engineer-ing association or supportive individual engineers, the local building department, and key local government offi cials and legislators.

Th e City of Los Angeles, adjacent to the City of Long Beach and with a population over three million, launched the largest manda-tory local government retroactive seismic safety program in the United States, when the City Council passed an ordinance in 1981. Th e law required structural upgrading, or demolition, of 14,000 unreinforced masonry buildings, excepting residential buildings that had four or fewer dwelling units.30 Th e 1985 Mexico City earthquake that caused over 10,000 deaths motivated

the Los Angeles City Council to accelerate the time table for compliance, and by the time of the 1994 Northridge earthquake in Los Angeles, most URM buildings subject to the ordinance had been retrofi tted.

Th e 1994 earthquake caused strong ground motion over Los Angeles and other cities of the region and “provided one of the fi rst major tests of the performance of retrofi tted unreinforced masonry (URM) buildings, and once again pointed out the vulnerability of URMs that have not been strengthened…. As would be expected,

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 27

unretrofi tted URM buildings performed worse, in general, than both reinforced masonry buildings and retrofi tted URM buildings. As observed in previous earth-quakes, many of these buildings suff ered signifi cant structural damage and posed serious risks to life safety.”31 Th ese statements pertain to unreinforced brick build-ings. Th e region also had some very old and historic adobe buildings, and the same engineering report just cited noted: “Historic adobe buildings in the Los Angeles area suff ered a tragic loss.” Th ese buildings, which are present in other Western and Southwestern states, have unique structural features, including the diff erent material properties of the adobe walls and their usually larger thickness, and they require their own engineering retrofi t approaches, diff erent from those used on the more common brick building.

Th e large-scale program enacted by the Los Angeles ordinance catalyzed the involvement of a wide spectrum of the community, many of whom initially opposed the idea because of cost. Th e key to its eventual success may lie with three sets of proponents. Th ese include its earliest advocates, the structural engineers of the region, who knew how great the risks were. With funding from the National Science Foundation, tests and analyses were conducted to develop a hazard reduc-tion package of retrofi t measures. Th e goal was not to bring these old buildings up to current code standards—which would be virtually an impossible task and prohibitively expensive—but to bring them up to a reasonable level of safety. Th e performance of buildings retrofi tted to that standard in the 1994 Northridge earthquake was generally in line with that criterion, although building owners often did not understand that “hazard reduction” could be compatible with a level of damage that required expensive repairs.

Th e Los Angeles Department of Building and Safety also played an essential role in this program. Th is agency reviewed a large volume of building evaluation reports submitted by consulting engineers and approved retrofi t design documents, once the program was underway. It was also responsible for reporting to the City Council on costs and progress and for initiating any legal actions against non-compliant owners.

Th e third source of crucial support was the Los Angeles City Council, which remained determined in passing an unpopular law. One legislator in particular, Howard Berman, maintained progress on the eff ort over a span of decades.

San Luis Obispo, California: Making the Effort to Communicate with Building Owners

The goal of working toward seismic safety

was combined with efforts by local agencies to support the economic development of the affected businesses.

Th is central California city passed its unrein-forced masonry law in 1992, taking the approach of setting deadlines for mandatory retrofi tting. Buildings were put into two categories, with the higher occupancy buildings having closer deadlines. Partial upgrades could be implemented, in order to extend the time permitted to come into full compliance. After

the nearby 2003 San Simeon earthquake, the city decided to accelerate retrofi ts of the remaining 40 unreinforced masonry buildings, which were clustered in the central business district. In the meantime, the state’s unreinforced masonry law required posting a standard hazard warning on unretrofi tted unreinforced

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28 Examples of Successful Risk Reduction Programs

masonry buildings. As the deadlines approached, the downtown business associa-tion and individual owners became more opposed to and concerned about manda-tory retrofi ts. Rather than wait until confl icts fl ared, the city retained an Economic Development Manager, who met individually with building owners to explain requirements and to inform them of technical assistance and fi nancial incentives available.32 Th e original deadline for all of the buildings to be in full compliance was 2018; it has since been moved to 2012. Twenty years would seem like a reason-able timetable for compliance but in fact, many business owners ignored the program in its fi rst decade and only seriously considered the law’s requirements when the time remaining had grown short.

Th e City’s eff ort to incorporate an economic development perspective into its pro-gram, rather than a building safety enforcement approach alone, is a lesson that may well be applicable elsewhere. Another lesson is that allowing a long lead time before the fi rst deadline for compliance comes due can result in a program getting off to a slow start.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 29

5 Additional Technical Background on Unreinforced Masonry Construction

Unreinforced masonry buildings have design and construction characteristics that make them perform poorly in earthquakes. Various retrofi t techniques

are available to reduce their risk, ranging from low-cost solutions like anchor-ing masonry parapets to highly engineered solutions involving seismic isolation. This chapter details typical construction characteristics, conceptual information about the earthquake response of URM buildings, and possible retrofi t solutions.

Out-of-plane forces act on a wall both inwardly

and outwardly, primarily causing bending (fl exural) stresses. In-plane forces, oriented parallel with the wall, cause sliding or shear stresses.

Masonry materials are intrinsically strong when compressed under the usual gravity loads but are weak in resisting earthquake forces, which make materials fl ex and also shear; ‘shear’ describes the tendency for a portion of the wall to slide vis-à-vis the rest. When an earthquake shakes an unreinforced masonry building, it causes the building’s walls to fl ex out-of-plane (see Figure 24) and to shear in-plane (see Figure 25). Unreinforced masonry is weak in resisting both of those types

of forces. Mortar is the “glue” that holds the masonry units together; however, when it eventually cracks, it does so in a brittle manner, similar to the way that the bricks crack. Generally speaking, older masonry construction was built using much weaker mortar than current building codes require. Mortar also tends to deteriorate in strength over time more than the masonry units themselves do. Th us, earthquake engineers sometimes say that in old masonry buildings, “the mortar holds the bricks apart, not together.”

Figure 25. In-plane failure of unreinforced masonry walls. —Rutherford and Chekene

Figure 24. Out-of-plane failure of unreinforced masonry walls. —Rutherford and Chekene

Shaking parallel to wall

Shaking perpendicular to wall

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30 Additional Technical Background on Unreinforced Masonry Construction

A common type of unreinforced masonry wall in one- or two-story buildings is approximately a foot thick and uses a pattern of brickwork called “American bond.” In this pattern, most of the bricks are laid running parallel with the wall (these are known as stretchers). Approximately every sixth horizontal row, there will be a row of bricks with their ends rather than their sides visible (these are known as headers), as illustrated in Figure 7 and Figure 8. Th e header courses extend into the cross-sec-tion or thickness of the wall, and they provide a strong clue that the wall is unrein-forced (because there is no empty space in the middle of the wall, where reinforc-ing and grout could have been placed). A form of hollow cavity unreinforced brick wall also exists, which has no bricks connecting outer and inner layers. Th is type of masonry work is done to provide some insulation and to keep rainwater from seeping through from the outside to inside of a building. Th ere are many patterns of brickwork, although American bond is the most common one. While engineers and building departments evaluate the strengths of unreinforced masonry walls on their individual merits, all unreinforced masonry walls are essentially “guilty until proven innocent,” when it comes to earthquake resistance. Simple fi eld testing methods can be used to measure existing masonry strength without damaging the wall.

Unreinforced masonry, as the name implies, is masonry without reinforcing. “Reinforcing” (see Figure 26) has a very specifi c meaning in this context. It refers to steel reinforcing bars (rebar), which vary in diameter from approximately 3/8 inch in diameter (9.5 mm, called a #3 bar) to an inch (25 mm) or more in diam-eter. A bar 4/8 inch in diameter is called a #4 bar, and so on. Th e bars have knobs or ridges along their length to increase their adhesion or bond with concrete or grout. Grout is essentially a very fl uid form of concrete, with small pea-sized gravel instead of the larger aggregate in concrete.

A reinforced masonry wall has a grid of horizontal and vertical steel reinforcing bars within the wall cross-section (see Figure 27). In reinforced brick construction, a hollow cavity is formed between an outer stack or wythe of bricks and an inner wythe, and the reinforcing is placed in this space. Grout is poured into the cavity, and when it sets, a monolithic structural sandwich forms, which is strong in resist-ing horizontal earthquake forces, both those forces perpendicular to and those parallel to the wall.

Figure 26. A piece of #4 bar (a steel reinforcing bar that is 4/8 inch in diameter). A nickname for reinforcing bar is rebar.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 31

Ductility is the toughness of a material—its ability to

crack or permanently bend out of shape, while still maintain-ing its structural integrity.

Reinforced masonry walls are not only much stronger than unreinforced ones: they also remain intact and stable, even if they are shaken to the point at which cracking occurs. Th at desirable property of ductility is one of the most important seismic requirements for all kinds of construction. Unreinforced

masonry, which lacks ductility, often comes apart in a brittle manner and col-lapses, when it is shaken severely and begins to crack.

How Do Unreinforced Masonry Buildings Behave in Earthquakes?

Th e short answer to this question is that unreinforced masonry buildings, on aver-age, perform very poorly in earthquakes. More than any other kind of construc-tion, they can be singled out as being seismically vulnerable. Th e following points clarify why this is so.

Inertial forces are caused by rapid movements—the quick

speeding up, slowing down, or turning of a car, for example—or the rapid and erratic shak-ing of the ground to which the building is connected.

When shaken in an earthquake, the heavy mass of masonry walls contributes to high earthquake forces. If you hold an empty cardboard box and shake it, then you don’t feel much eff ect. Fill it with groceries, though, and shake it, and you experience large inertial forces, because the mass is now greater. Inertial forces are the product of the mass of an object and the acceleration of its

motions; thus, heavier (more massive) buildings generate higher forces when they are shaken. Acceleration indicates how much an object speeds up, slows down, or changes direction. Drop an object here on Earth, and it falls with an acceleration of 1 unit of gravity, 1 g. Shake the ground horizontally with an acceleration of 1 g, and an object that is rigidly mounted to it experiences a sideways force that is equal to its own weight. Accelerations of ½  g up to 1 g or more have been measured in earthquakes. It is easy to understand why people can’t stand up during strong earthquake shaking, when you imagine yourself subjected to horizontal, erratic pulls equal to half or more of your body weight.

Acceleration is a com-mon measure of the

severity of earthquake shaking.

Figure 27. Reinforced brick wall. —FEMA 154, Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook

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32 Additional Technical Background on Unreinforced Masonry Construction

As a rough guide, when strong-motion seismographic instruments measure accel-erations of ground shaking to be about one to two tenths of that of gravity (0.1 g to 0.2 g), then earthquake-resistant construction may suff er cracking but no seri-ous damage. However, unreinforced masonry buildings can experience signifi cant damage and may drop debris, such as parapets. As shaking severities approach ½  g or even exceed 1 g, then damage to all kinds of construction is common, but it is especially severe for unreinforced masonry buildings. Th e building code allows the structure to deform so much in a severe earthquake that it no longer elastically returns to its pre-earthquake position and condition. Keeping it “earthquake-proof”—that is, able to undergo strong shaking without experiencing even minor damage—would require prohibitively expensive protection for the structure and for nonstructural components such as ceilings, partitions, piping, etc. Modern buildings designed to recent building codes have successfully resisted the most severe earthquake ground motions with only repairable damage. For most kinds of modern, code-conforming construction, less than 5% is severely damaged or performs in a hazardous manner in a strong earthquake, whereas more than half of unreinforced masonry buildings typically receive that level of damage (see Chapter 2).

A cardboard box with a lid can resist much higher sideways or lateral forces than the same box without the top can resist. Building walls also need that “lid on the box,” in order to stabilize them. Th at role is provided by the roof and any fl oors above ground level. Floor and roof diaphragms hold the walls of a building together.

Diaphragm is the term struc-tural engineers use to refer

to fl oors or roofs in their roles of resisting horizontal, rather than the usual vertical, forces.

Th e most common kind of fl oor and roof in an unreinforced masonry building is wood frame, typically “two-by” lumber such as 2 × 10 small beams (joists), which are usually sheathed with “one-by” boards (the use of plywood not being common until after World War II in building

construction). Th e wood fl oor or roof diaphragm of a building is, unfortunately, very fl exible when compared to the stiff er masonry walls. Th is fl exible wooden diaphragm can allow building walls to lean or bow excessively either inwardly or outwardly (out-of-plane). As the diaphragm bends sideways and vibrates back and forth, it dynamically pushes and pulls on the brick walls, increasing their motions and damage.

Individual structural elements, such as a wall and the roof, only perform ade-quately in earthquakes when these elements are strongly connected. Th e typical connection of the wood beams or joists to the unreinforced masonry walls, how-ever, is very weak. A common construction detail used over the decades was to rest the end of a beam in a pocket or niche in the brick wall, with little or no steel hardware providing a strong, positive connection. When an unreinforced masonry building is shaken, the roof or fl oor framing can pull away from the walls. Th e walls need the roof to keep them from leaning too far and collapsing, while the roof needs the walls to support it, in order to keep from falling. Typical unrein-forced masonry damage includes both the collapse of heavy masonry wall areas and the collapse of part or all of the roof or upper fl oors (see Figure 28).

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 33

Chapter 2 previously mentioned the common presence of parapets, chimneys, and cornices or other decorative features on unreinforced masonry buildings. Th ese elements do not play a structural role, but their failure can be very hazardous.

Th e fact that unreinforced masonry buildings often have multiple seismic weak-nesses is not surprising—they were not designed to be seismically safe in the fi rst place. By the time when American building codes started to include seismic requirements, fi rst in California in the 1930s and slowly spreading nationwide, reinforced masonry construction techniques became increasingly standard. Strong steel connections, analysis of the overall load path that the structural elements needed to provide, and an emphasis on ductility also became increasingly stan-dard.

Th us, unreinforced masonry buildings not only have three strikes against them from an earthquake engineering point of view—they are vulnerable for at least twice as many reasons:

1. Th e walls are weak in resisting horizontal forces (and they lack ductility or toughness);

2. Th e walls are heavy (they have high mass, leading to high inertial forces);

3. Diaphragms are excessively fl exible (insuffi cient lateral support for the walls);

4. Diaphragm-to-wall connections are either absent or weak;

5. Parapets and ornamentation are common (and made of masonry), and;

6. Th e buildings were not seismically designed by an engineer (because they were built prior to the time when seismic regulations pertaining to masonry began to be enforced in that particular region).

Figure 28. Failure of roof-to-wall connection, with resulting collapse. —Rutherford and Chekene

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34 Additional Technical Background on Unreinforced Masonry Construction

How Are Unreinforced Masonry Buildings Seismically Retrofi tted?

Retrofi tting or seismically upgrading a building, which means reconstructing portions of it, in order to improve its earthquake resistance, is not the only way to reduce risks. A building that is demolished obviously poses no further risk. One that has its occupancy changed to a lower level—for example, from a theater to a warehouse—also reduces the risk of injury. Th e risk of economic loss might be reduced by purchasing earthquake insurance (although it is often unavailable or very expensive for this kind of construction). In this document, however, risk reduction through structural seismic retrofi t (also referred to as rehabilitation) is the focus.

A variety of retrofi t measures have been included in unreinforced masonry building risk reduction programs, and one or more of those measures may be appropriate in a given case. Th e FEMA book, Techniques for Seismic Rehabilitation of Existing Buildings (FEMA 547), provides examples that relate to several kinds of construction, including unreinforced masonry bearing wall buildings.33 Th e general standard for such retrofi t measures in the United States is the International Existing Building Code.34 Th e International Code Council (ICC) was formed in 2000 through the merger of the three previous model building code organizations: the Building Offi cials and Code Administrators (BOCA), which promulgated the National Building Code; the International Conference of Building Offi cials (ICBO), which promulgated the Uniform Building Code (UBC), and; the Southern Building Code Congress International (SBCCI), which promulgated the Standard Building Code. Prior to the establishment of the ICC code for existing buildings, the model code available with specifi c application to seismic retrofi t projects was “Seismic Strengthening Provisions for Unreinforced Masonry Bearing Wall Buildings,” the Uniform Code for Building Conservation (UCBC) Appendix Chapter 1, 1997 edition, which was cross-referenced with the 1997 Uniform Building Code. In some cases, a local program may still use the Uniform Code for Building Conservation rather than the newer ICC document. Over time, it is expected that adopted versions of build-ing codes will standardize around the ICC codes and the standards that it incorpo-rates by reference.

Usually retrofi t that off ers the biggest benefi t relative to its costs is the anchorage of masonry parapets, those short walls that extend a few feet above a building’s roofl ine. Bracing or removing these parts of the building, along with other exterior masonry appendages such as cornices, eff ectively addresses the type of damage that can happen even in very light shaking. Th e most common type of bracing used is to bolt diagonal steel struts to the top of the parapet, with the bottom end of the struts anchored with bolts into the roof structure. Usually this does not change the building’s appearance from the street (see Figure 29).

Parapet safety programs do not provide protection, however, against the collapse of the building itself. Th e fi rst additional increment of seismic protection, beyond parapet and appendage bracing, is provided by bolting the walls to the roof and to any fl oors above the ground fl oor level. Long steel bolts are typically inserted into holes drilled in the wall and attached to a steel angle, which in turn is bolted to the side of a wooden joist. Th e end of the bolt on the outside of the wall requires a large washer (the size of a teacup saucer) to prevent it from pulling through in an earthquake (see Figure 30). In many communities that have enacted seismic ret-

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 35

rofi t ordinances, the row of these washers running along the roofl ine indicates the presence of this kind of retrofi t. Similar-looking steel washers may be part of an older building’s construction. In general, old, pre-seismic-code wall-joist anchors are not found to be adequate.

Th e next additional increment of earthquake protection is provided by conducting a more thorough engineering examination of the entire building structure. Th is examination might reveal the need to increase the horizontal stiff ness of fl oors and the roof, which is typically accomplished by adding a layer of sheathing (sheets of plywood or oriented-strand board). New columns (posts) may be added that can hold up the fl oors and roof, even if portions of the bearing wall fail. Th e brick or concrete block walls themselves cannot be transformed into modern reinforced masonry construction. However, walls can be strengthened by several techniques, making them stronger, even if not as strong as new, reinforced masonry walls. One available technique is to add a layer of reinforced concrete to the inside or outside of the wall, as shown in Figure 31.

Strongbacks are vertical “splints” that retrofi t

a wall to increase its out-of-plane resistance to horizontal forces.

Another approach is to install columns attached to the walls, which act like splints or strongbacks that brace the wall against excessively bowing outward or inward (see Figure 32). Yet another wall strengthening method is to drill holes down through the wall from top to bottom, using machinery adapted from the oil well industry to

insert a steel bar and grout. Interior partitions can also help to stiff en the overall box structure and can damp out or absorb its vibrations. Each retrofi t brings its

Figure 29. Retrofi t bracing of an unre-inforced masonry parapet. Typically, diagonal bracing struts are installed behind the wall and anchored to the roof, as shown here, which makes them unobtrusive. —Federal Emergency Management Agency

Figure 30. Generic wall-diaphragm connection retrofi t detail. —FEMA 547, Techniques for the Seismic Rehabilitation of Existing Buildings

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36 Additional Technical Background on Unreinforced Masonry Construction

own challenges. For example, a church with an unreinforced masonry spire may need to insert steel trusswork inside the tower to brace it adequately.

Seismic isolation devices can be employed in combination with any of the above techniques. Th ese devices are “shock absorbers” manufactured for the specifi c purpose of being installed between a building’s superstructure and foundation; they soften and reduce the motion of the ground, as it comes up into the building structure. Prominent examples of this kind of retrofi t being applied to prominent historic buildings that contain unreinforced masonry include the Salt Lake City and County Building and San Francisco City Hall (see Figure 33).

One can’t simply take the building code regulations for new buildings and extract particular features to guide the retrofi tting of existing buildings. In fact, these kinds of retrofi ts require design criteria developed specifi cally for existing build-ings. Th e Uniform Code for Building Conservation and the ICC International Existing Building Code evolved to meet that need. Local communities have also adopted a number of diff erent code rules for unreinforced masonry retrofi ts; some of these are described in Chapter 4. Codes also typically have “triggers” that require much more signifi cant overall building upgrading if a building remodel exceeds a par-ticular threshold. For example, code requirements might be triggered if the cost of the new work exceeds some percentage of the value of the existing building.

Figure 31. California Capitol Retrofi t.An exhibit shows a cut-away view of the reinforced concrete that is anchored into the brickwork with epoxied reinforcing bars. —Robert Reitherman

Figure 32. A retrofi tted lateral-force-resisting post (strongback). The strongback column spans from foundation to roof, serving to brace a brick wall against out-of-plane forces. —Consortium of Universities for Research in Earthquake Engineering

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 37

Th ese requirements may address concerns beyond the seismic safety concern that motivated an earthquake retrofi t. Issues such as handicapped access, exits, energy conservation, removal of hazardous materials such as asbestos, and so on can come into play. Deciding on the level of required seismic retrofi tting that is appro-priate relative to its associated costs is a big part of developing any risk reduction program.

Retrofi ts require an engineer’s expertise to design the changes to the construc-tion. Th ere are many kinds of engineer; in this instance, we are referring to civil engineers with structural engineering expertise. In some states, “structural engineer” is a license or professional registration category, while in other states, the term is used more generically. Seismic retrofi ts are signifi cant remodels that require building permits, and thus building departments must review plans and issue permits. Th e technical community—the consulting structural engineers, building departments, architects, and contractors—are essential to any successful unreinforced masonry building risk reduction program, but they can’t implement such measures by themselves. Th e guidance in Chapter 3, “Developing a Strategy for Implementing a URM Risk Reduction Program,” and in Chapter 4, “Examples of Successful Risk Reduction Programs,” makes it clear that key non-technical sectors of the community must be involved and exert leadership.

Figure 33. The San Francisco City Hall seismic retrofi t, which includes seismic isolators. —Robert Reitherman

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38 Additional Technical Background on Unreinforced Masonry Construction

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 39

6 Sources of Information

In addition to the cited references, the following sources of information may be useful to consult for further information.

Note that all of the documents published by FEMA listed here are available as downloads and can often be mailed in printed form, upon request. A much larger number of earthquake publications than are listed here are available from FEMA. See: http://www.fema.gov/plan/prevent/earthquake/.

Publications for the General Public

California Seismic Safety Commission, “Status of the Unreinforced Masonry Building Law: 2006 Progress Report to the Legislature,” California Seismic Safety Commission, Sacramento, California; http://www.seismic.ca.gov/pub.html.

In concise form, this report indicates the types of programs being used in California and their success rates.

Oregon Department of Land Conservation and Development, Natural Hazard Technical Resource Guide, Salem, Oregon, July 2000; http://oregon.gov/LCD/HAZ/docs/earthquakes/08_seismic.pdf.

Th is booklet explains to the public the nature of the various natural hazards in Oregon and what is being done about them. Examples of programs to reduce the earthquake hazards of existing buildings are included, along with a review of legislative bills that were drafted to require seismic inventories of buildings. It points the reader toward fur-ther sources of information.

Utah Seismic Safety Commission, “The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings” (n.d.); http://ussc.utah.gov/utahseismic.

Th is booklet exists as a web-based document for the general public. It promotes the idea of producing web-accessible public information prod-ucts as part of a seismic risk reduction program, with the twin advan-tages of lowering costs (eliminating printing and distribution costs once the document is produced) and appealing to the increasing number of people who turn to the web as their fi rst source of information. It may also be advisable to have printed versions of such documents available, for example, to hand out at meetings, to reach those who do not usually use the web, and to reach additional audiences such as those who pick up a copy when waiting at the counter of a building or planning department.

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40 Sources of Information

Utah Seismic Safety Commission, “Putting Down Roots in Earthquake Country: Your Handbook for Earthquakes in Utah,” 2008; http://ussc.utah.gov.

Th is booklet is a customized version of a publication developed for California residents by the Southern California Earthquake Center, the U.S. Geological Survey, and the Federal Emergency Management Agency. It includes an explanation of the hazard of earthquake shaking and fault rupture in Utah and information on unreinforced masonry.

Historic Buildings and Seismic Retrofi ts

California Historical Building Code (Part 8, Title 24 of California law), California Building Standards Commission, 2007; http://www.dsa.dgs.ca.gov/SHBSB/default.htm.

Th is is the generally prevailing code used for historical buildings in California, though not required statewide, and is now correlated with the provisions of the 2006 International Building Code. It allows more latitude in seismic retrofi tting of historic buildings than apply to non-historic building projects.

Rachel Cox, Controlling Disaster: Earthquake-Hazard Reduction for Historic Buildings, National Trust for Historic Buildings, Washington, DC 2001; http://www.preservationbooks.org.

An introduction to the topic and guide to further resources.

Building Inventories and Evaluation of Existing Buildings

American Society of Civil Engineers, Seismic Evaluation of Existing Buildings—ASCE 31-03, Reston, Virginia, 2002; ordering information: http://pubs.asce.org/books/standards/.

Th is standard was developed for the use of structural engineers and building departments in applying consistent criteria and calculation methods to the seismic evaluation of existing buildings, that is, the process of deciding whether an existing building is defi cient in particular ways and requires strengthening. It covers all kinds of buildings.

Applied Technology Council, Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook—FEMA 154, second edition, Federal Emergency Management Agency, Washington, DC, 2002; http://www.fema.gov/plan/prevent/earthquake/.

A guide to the subject concerning all types of buildings, but with a chap-ter specifi c to unreinforced masonry bearing wall buildings. Includes sample data collection forms and guidance on fi eld methods to identify unreinforced masonry buildings.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 41

Building Codes, Standards, Guidelines, and Laws Applicable to Existing Buildings

American Society of Civil Engineers, Seismic Rehabilitation of Existing Buildings—ASCE/SEI 41/06, Reston, Virginia, 2007; ordering information: http://pubs.asce.org/books/standards/.

Th is standard was developed for use by structural engineers and build-ing departments after the decision is made to strengthen (rehabilitate) a building, and it is not limited to unreinforced masonry. It includes guid-ance to the engineer on how to give appropriate earthquake engineering “credit” to older kinds of structural components that are not included in modern building codes and how to analyze them. Forerunner publi-cations to this standard include documents known as FEMA 273, and FEMA 356.

Association of Bay Area Governments, Seismic Retrofi t Incentive Programs, Oakland, California; http://www.abag.ca.gov/bayarea/eqmaps/incentives

Th is report focuses on incentives, but it also includes summaries of sev-eral local government ordinances.

California Seismic Safety Commission, “Status of the Unreinforced Masonry Building Law: 2006 Progress Report to the Legislature,” California Seismic Safety Commission, Sacramento, California; http://www.seismic.ca.gov/pub.html.

Includes a summary of this state law, passed in 1986. Also mentioned above, under Publications for the General Public.

International Code Council, International Existing Building Code, 2006 edition, Washington, DC; ordering information: http://www.iccsafe.org/

Th is is derived from the earlier Uniform Code for Building Conservation, which may still be the locally applicable standard, depending upon the jurisdiction.

Rutherford & Chekene, Techniques for the Seismic Rehabilitation of Existing Buildings—FEMA 547, Federal Emergency Management Agency, October 2006; http://www.fema.gov/plan/prevent/earthquake/.

Written for engineers and building department personnel, this manual deals in Chapter 21 with specifi c retrofi t measures for unreinforced masonry buildings, ranging from bracing parapets and veneer to reinforced concrete and fi ber-reinforced polymer methods of strengthening walls. Includes generic engineering details of the various retrofi t alternatives.

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42 Sources of Information

Uniform Code for Building Conservation, Appendix Chapter 1, International Code Conference, Washington, DC, 1997; ordering information: http://www.iccsafe.org/

Originally published by the International Conference of Building Offi cials, the organization promulgating the Uniform Building Code, prior to the merger of model code organizations into the International Code Council. Th e Uniform Code for Building Conservation is formatted to be compatible with the 1997 Uniform Building Code.

Costs of Seismic Retrofi ts

Federal Emergency Management Agency, “FEMA Seismic Rehabilitation Cost Estimator,” FEMA Seismic Rehabilitation Cost Estimator; http://www.fema.gov/srce/index.jsp

Th e user of this web-based calculator can either use a simplifi ed method requiring little input information or a more advanced method that requires selections among more variables.

Hart Consultant Group, Inc., Typical Costs for Seismic Rehabilitation of Buildings, Volume 1, Summary—FEMA 156, and Volume 2, Supporting Documentation—FEMA 157, Federal Emergency Management Agency, Washington DC, 1994-1995, second edition; http://www.fema.gov/plan/prevent/earthquake/.

A study of completed seismic upgrade projects to derive cost statistics.

Rutherford & Chekene, Seismic Retrofi tting Alternatives for San Francisco’s Unreinforced Masonry Buildings: Estimates of Construction Cost and Seismic Damage, San Francisco Department of City Planning, 1990.

A study which grouped the city’s 2,000 unreinforced masonry buildings into categories based on occupancy, size, and confi guration, in order to estimate what kinds of retrofi ts would be needed to meet alternative proposed strengthening criteria, listed with associated costs.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 43

7 End Notes and Cited References

1. Th e International Building Code, promulgated by the International Code Council, obtains its seismic criteria for where particular types of structural systems can be used from ASCE 7-05, Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-05 including Supplement No. 1), American Society of Civil Engineers, Reston, Virginia, 2006. Th e map in Figure 1 of this document is based on several assumptions, including: (1) Occupancies up through III in Table 1-1 of ASCE 7-05, which does not include fi re stations, hospitals, or other essential facilities; (2) a short-period site coeffi cient, Fa, of 1.75 (Table 11.4-1), based on the mapped short-period Maximum Considered Earthquake (SS); and (3) the design spectral short-period accelerations (SDS) must be less than 0.33 for Seismic Design Category B to apply (Table 11.6-1), and with the above assumptions, the maximum SS of 0.33 is rounded here to 0.3 for mapping pur-poses. For essential occupancies or for very soft soil, the red areas on the map would expand.

2. Architectural Resources Group, An Assessment of Damage Caused to Historic Resources by the Loma Prieta Earthquake, National Trust for Historic Preservation, Washington, DC, August 1990, p. 40.

3. Th e Federal Emergency Management Agency has published a number of pub-lications that deal with a variety of kinds of buildings, and also for utility and transportation systems. See http://www.fema.gov/plan/prevent/earthquake/. FEMA publication number 736, “Catalog of FEMA Earthquake Resources,” available at that website, provides the complete list.

4. Statistics are compiled from the 1886 Charleston, 1906 San Francisco, 1925 Santa Barbara, 1933 Long Beach, 1971 San Fernando, and 1983 Coalinga earthquakes, in districts where the Modifi ed Mercalli Intensity was approxi-mately VII or greater. Data for the 1886 Charleston earthquake from H.C. Stockdell, H. C. et al., Record of Earthquake Damages, Winham & Lester Publishers, Atlanta, Georgia, 1886. Data for the 1925 Santa Barbara earth-quake in Karl V. Steinbrugge, Earthquakes, Volcanoes, and Tsunamis: An Anatomy of Hazards, Skandia America, New York, New York, 1982, p. 306. Data for the other earthquakes from the compilation in Robert Reitherman, “Seismic Damage to Unreinforced Masonry Buildings,” Final Report to the National Science Foundation, Scientifi c Service, Inc., Redwood City, California, 1984, p. 23.

5. H.C. Stockdell, et al., Record of Earthquake Damages, Winham & Lester Publishers, Atlanta, Georgia, 1886; fi gure for the demolitions from John R. Freeman, Earthquake Damage, McGraw-Hill, New York, New York, 1932, p. 284.

6. Karl Steinbrugge, Earthquakes, Volcanoes, and Tsunamis: An Anatomy of Hazards, Skandia America Group, New York, 1982, p. 306.

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44 End Notes and Cited References

7. C. D. Wailes and A. C. Horner, “Earthquake Damage Analyzed by Long Beach Offi cials,” Engineering News-Record, May 25, 1933.

8. Robert Reitherman, Gregor Cuzner, T.C. Zsutty, and Gretchen Smith, “Performance of Unreinforced Masonry Buildings,” Coalinga, California, Earthquake of May 2, 1983, Earthquake Engineering Research Institute, Oakland, California, 1984, p. 132.

9. Architectural Resources Group, An Assessment of Damage Caused to Historic Resources by the Loma Prieta Earthquake, National Trust for Historic Preservation, Washington, DC, 1990, p. 29.

10. Nisqually Earthquake Clearinghouse Group, Th e Nisqually Earthquake of 28 February 2001: Preliminary Reconnaissance Report, p. 11.

11. California Seismic Safety Commission, “Findings and Recommendations from the San Simeon Earthquake of December 22, 2003,” California Seismic Safety Commission, Sacramento, California; http://www.seismic.ca.gov/pub.html.

12. Federal Emergency Management Agency, “FEMA Seismic Rehabilitation Cost Estimator,” http://www.fema.gov/srce/index.jsp.

13. Hart Consultant Group, Inc., Typical Costs for Seismic Rehabilitation of Buildings, Volume 1, Summary—FEMA 156, and Volume 2—FEMA 157, Supporting Documentation, Federal Emergency Management Agency, Washington DC, 1994-1995, second edition; http://www.fema.gov/plan/prevent/earthquake/.

14. Applied Technology Council, Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook—FEMA 154, second edition, Federal Emergency Management Agency, Washington, DC, 2002; http://www.fema.gov/plan/pre-vent/earthquake/.

15. Robert Olshansky, “Making a Diff erence: Stories of Successful Seismic Safety Advocates,” Earthquake Spectra, Volume 21, No. 2, May 2005; http://www.urban.illinois.edu/faculty/olshansky/index.html.

16. Th e Utah law; http://www.dopl.utah.gov/laws/R156-56.pdf.

17. Th e Utah resolution H.J.R. 7; http://le.utah.gov/~2008/bills/hbillenr/hjr007.pdf.

18. Personal communication from Barry Welliver, former Chair, Utah Seismic Safety Commission, June 23, 2009.

19. California Seismic Safety Commission, “Status of the Unreinforced Masonry Building Law: 2006 Progress Report to the Legislature,” California Seismic Safety Commission, Sacramento, California; http://www.seismic.ca.gov/pub.html.

20. Th e original referenced standard was the Uniform Code for Building Conservation, Appendix Chapter 1, published by the International Conference of Building Offi cials. After the three U.S. model code groups merged in 2000 to form the International Code Council and to promulgate the International Building Code, the relevant existing building code became the International Existing Building Code of 2006.

21. Historic Architecture, Seattle, Washington; http://www.historicseattle.org/advo-cacy/nisqually.aspx.

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 45

22. Levy Oversight Committee, “Status Report, July 17 2008,” Fleets and Facilities Department, City of Seattle, Washington; http://www.seattle.gov/fl eetsfacilities/fi relevy/about.htm.

23. Robert Olshansky, “Making a Diff erence: Stories of Successful Seismic Safety Advocates,” Earthquake Spectra, Volume 21, No. 2, May 2005; http://www.urban.illinois.edu/faculty/olshansky/index.html.

24. Yumei Wang and Bill Burns, “Case History on the Oregon GO Bond Task Force: Promoting Earthquake Safety in Public Schools and Emergency Facilities,” Proceedings of the 8th National US Earthquake Conference, Earthquake Engineering Research Institute, Oakland, California, 2006; http://www.oregon-geology.org/sub/projects/rvs/EERI-GO-Bond-text.pdf.

25. Real Property Transfer Tax—Seismic Retrofi t Fund, City of Berkeley; http://www.ci.berkeley.ca.us/ContentDisplay.aspx?id=6282.

26. Association of Bay Area Governments, Seismic Retrofi t Incentive Programs, Oakland, California; http://www.abag.ca.gov/bayarea/eqmaps/incentives.

27. Daniel Barclay, “Assessing Seismic Safety Policy,” Massachusetts Institute of Technology Undergraduate Research Journal, Volume 10, Spring 2004; http://web.mit.edu/murj/www/v10/v10-Features/v10-f2.pdf.

28. Edward M. O’Connor, ““An Interview With Edward M. O’Connor: Retroactive Regulations in Long Beach,” Robert Reitherman, interviewer, Building Standards, International Conference of Building Offi cials, September-October, 1984.

29. Association of Bay Area Governments, Seismic Retrofi t Incentive Programs, Oakland, California; http://www.abag.ca.gov/bayarea/eqmaps/incentives/. See pages 25-34.

30. Daniel Alesch and William Petak, Th e Politics and Economics of Earthquake Hazard Mitigation: Unreinforced Masonry Buildings in Southern California, Natural Hazards Center, University of Colorado, Boulder, 1986; http://www.colorado.edu/hazards/publications/monographs/monopubs.html - 1980.

31. William T. Holmes and Peter Somers, editors, Northridge Earthquake of January 17, 1994 Reconnaissance Report—Volume 2, Earthquake Spectra, supplement C to Volume 11, January 1996, p. 195-217.

32. City of San Luis Obispo, “Unreinforced Masonry Hazard Mitigation Program,” http://www.ci.san-luis-obispo.ca.us/economicdevelopment/seismiccoord.asp; City Manager, City of San Luis Obispo, “Draft Outline of Seismic Safety Ordinance Update,” http://www.prcity.com/government/citycouncil/agenda-items/2004/March/2004 03-16 CC ITM 17.pdf.

33. Rutherford & Chekene, Techniques for the Seismic Rehabilitation of Existing Buildings—FEMA 547, Federal Emergency Management Agency, October 2006; http://www.fema.gov/plan/prevent/earthquake/.

34. International Code Council, International Existing Building Code, 2006 edition, Washington, DC; ordering information: http://www.iccsafe.org/.

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46 End Notes and Cited References

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FEMA P-774: Unreinforced Masonry Buildings and Earthquakes 47

8 Project Participants

FEMA Project MonitorCathleen M. CarlisleFederal Emergency Management Agency500 C Street, SWWashington, DC 24072

Project ManagerTh omas R. McLane Applied Technology Council2111 Wilson Blvd., Suite 700Arlington, Virginia 22201

Principal AuthorsRobert K. ReithermanConsortium of Universities for Research in Earthquake Engineering1301 South 46th St., Building 420Richmond, California 94804

Sue C. PerryU.S. Geological Survey525 So. Wilson AvenuePasadena, California 91106

Project Review PanelRonald P. GallagherR P Gallagher Associates, Inc.519 17th Street, Suite 220Oakland, California 94612

Jon A. HeintzApplied Technology Council201 Redwood Shores Parkway, Suite 240Redwood City, California 94065

William T. HolmesRutherford & Chekene55 Second Street, Suite 600San Francisco, California 94105

Ugo Morelli2700 Calvert Street, NW, #314Washington, DC 20008

Lawrence D. ReaveleyUniversity of UtahDept. of Civil and Environmental Eng’g160 S. Central Campus Drive, Room 104Salt Lake City, Utah 84112-0561

Christopher RojahnApplied Technology Council201 Redwood Shores Parkway, Suite 240Redwood City, California 94065

EditorKristen Yawitz1923 Lyon AvenueBelmont, California 94002